Protein surface antigens (Ag) I/II and III of Streptococcus mutans have been implicated in protective immunity to dental caries. The objective of this proposal is to identify individual antigenic determinants of these antigens that may be important for inducing immunity without causing potentially harmful side effects. Further aims are to investigate the immunochemical structure and biological function of these antigens, in order to elucidate further the part played by S. mutans in the cariogenic process, and the mechanisms of immunity to it. A panel of monoclonal antibodies to Ags I/II and III will be developed and tested for their reaction with topographically distinct antigenic determinants in an inhibition radioimmunoassay. These will be used to identify antigenic fragments of Ags I/II and III generated by enzymatic and chemical cleavage, and separated by polyacrylamide gel electrophoresis, using "Western Blotting". Antigens and their fragments will be purified by immunoadsorbent chromatography and analysed chemically for amino acids and carbohydrates. Comparisons will be made between materials obtained from different serotypes of S. mutans, and from S. sanguis and recombinant clones of E. coli expressing S. mutans antigen genes. The purified fragments will also be used in assays of antibodies in the sera and saliva of experimental animals that have been immunized against S. mutans, and of human subjects, in order to examine whether the individual antigenic determinants are relevant to immunity to caries. The monoclonal antibodies (and conventional antisera) will also be used as inhibitors of surface-related and metabolic properties of S. mutans, such as adherence to surfaces, growth and acid production, in order to investigate the physiological functions of Ags I/II and III. The antigens will also be tested directly for their ability to interact with components of saliva.